There is a time stamp option in Transmission Control Protocol (TCP). When a TCP flow supports this option, a data packet header includes a record of a data packet transmission time. An implementation method is to place a tick count of a current system clock in a time stamp field when a sending party sends a packet segment. When confirming the packet segment, a receiving party copies a value of the time stamp field to a time stamp echo acknowledgement field. A time stamp (in ticks) is a value that increases monotonically. In a general TCP application, a receiving party only needs to echo back a received time stamp, but does not need to pay attention to a time stamp unit of a peer party, and does not require clock synchronization between the two connected parties, either. System clock frequencies used in operating systems and computers are mutually different. Therefore, time units of a tick count in different servers are also different, and may range from 0.5 millisecond to 1000 milliseconds.
A time stamp in the TCP protocol is just a tick count rather than an absolute time. Therefore, currently, the time stamp can be used locally only, and cannot be used by any remote device on a network.
A prior-art method for measuring a time stamp unit of a remote device is based on time synchronization between a remote end and a local end. In the method, a time stamp unit may be estimated, minus an error caused by a transmission delay, according to comparison between a packet receiving time and a packet header time stamp. In this method, time synchronization on a network is required, and a measurement error caused by the transmission delay cannot be effectively eliminated, resulting in inaccurate measurement.